Most passenger vehicles use a 3-point seatbelt as safety harness for restraining the occupants in the vehicles. This harness has a up-side-down “Y” shaped configuration. It has 3 mounting points. The first point is outboard lap mount, or anchorage point, while the second point is inboard lap mount, or buckle point, and the third point is the shoulder point, or D-ring point.
Many prior arts have at least one linear pretensioner connected to anchorage point (usually called PLP), or buckle point (usually called PBP), or both of the seatbelt. Two of these prior arts are U.S. Pat. No. 8,132,829, and 7,172,218.
Typical PLPs or PBPs have a pyrotechnic charge that is fired when a collision occurs, producing expanding gas which pressurizes a gas chamber within a tube, which forces a piston down the tube. The piston is connected to the belt system by a cable or strap. Movement of the piston tightens or “pretensions” the belt against the occupant.
In order to retract the cable, the cable is connected to the piston and is pulled into the expanding gas chamber. Sealing the gas chamber around the flexible cable presents a difficult challenge.
U.S. Pat. Nos. 7,823,924, 8,528,987, and 9,090,221 have shown some so-called cable-free pretensioners presenting a better concept overcoming the sealing challenge listed above by eliminating the cable.
But this technology or other known prior arts are not effective at utilizing the space of gas generator (or initiator). In other words, the axial dimension of apparatus by these technologies cannot be less than the stacking up of these three elements: the axial length of initiator, the axial length of piston, and the travel of piston (or so called actuating profile).